There has been proposed a developer cartridge, which accommodates developer, and which is mounted to an image forming apparatus such as a laser printer and to a developing unit of the image forming apparatus.
As an example of a related art developer cartridge, JP-A-2007-293268 discloses a toner box having a double structure including an inside housing for accommodating toner and an outside housing for accommodating the inside housing in such a manner as to rotate freely therein. The toner box is installed in a process unit of a laser printer.
In the toner box, the outside housing includes a first toner discharge opening, and the inside housing includes a second toner discharge opening. In the toner box, the inside housing is rotated relative to the outside housing (i.e., relative movement) so that the first toner discharge opening and the second toner discharge opening are made to confront each other for enabling communication between the first toner discharge opening and the second toner discharge opening in order to supply toner from the inside housing to the process unit.
In the toner box, first radial projections formed of an elastic material are provided around the second toner discharge opening on an external surface of the inside housing. When the second toner discharge opening is opened, the first radial projections are exposed partially from the first toner discharge opening to be brought into contact with the process unit. According thereto, the first radial projections can hold a space between the process unit and the inside housing airtight and fluid-tight. Therefore, a toner leakage from the second toner discharge opening may be prevented. That is, in the toner box, the first radial projections function as a seal member.